The objectives are to use the canine model of human mucopolysaccharidoses VII (MPSVII) to understand connective tissue pathogenesis and to develop and evaluate therapeutic strategies based on the uptake of normal enzyme by the mannose-6-phosphate receptor on deficient cells. Previously, we 1) determined the diseases to be caused by an arginine to histidine amino acid substitution causing deficient activity in the lysosomal enzyme beta-glucuronidase (GUSB), 2) characterized the clinical course and pathology, showing that, similar to children with MPS VII, the dogs are growth-retarded, have a facial dysmorphia, corneal clouding, thickened heart valves, a narrow trachea, deformed sternum, and synovial joints with progressive degenerative lesions of the articular cartilage such that dogs with MPS VII can not stand or walk by six months of age, 3) evaluated heterologous bone marrow transplantation (BMT) in young MPS VII dogs showing that the corneas were cleared, heart valve lesions improved, and that the dogs could stand, and run to at least six years of age, 4) successfully developed an ex vivo hematopoietic progenitor cell gene marking technique, and in vivo selection of transduced cells, in normal dogs using a retroviral vector, 5) performed enzyme replacement trials in MPS VII dogs, determining the distribution of enzyme and documenting an immune response to human GUSB prior to clinical improvement, 6) evaluated high level, stable, long-term production of canine GUSB by the liver in vivo using a retroviral vector that has produced a dramatic clinical improvement: clear corneas, absence of cardiac abnormalities, normal tracheal diameter, and dogs that can stand, and run to at least 14 months of age. The specific aims of the current proposal are to: 1) a. investigate the roles of apoptosis, metallo-proteinases, and nitric oxide production in the pathogenesis of articular cartilage pathology, and b. develop gene transfer to synovial joints by the intra-articular injection of adeno-associated viral vectors containing the canine GUSB cDNA, 2) continue and expand hepatocyte gene therapy by the intravenous administration of canine GUSB cDNA in a retroviral vector, and 3) adapt ex vivo hematopoietic progenitor cell gene transfer and in vivo selection for MPS VII in the dog. These studies will facilitate the understanding of pathogenesis and development of gene therapy for the human MPS disorders, and provide insight useful for therapy of other genetic diseases.